A FIFO is a standard implementation of a queue in which data is loaded into the FIFO in a sequence and unloaded from the FIFO in the same sequence in which it was loaded into the FIFO. Informational signals associated with a standard FIFO indicate different conditions of the FIFO, such as whether the FIFO is empty (i.e., whether there is no valid data in the FIFO) and whether it is full (i.e., whether there is no more room in the FIFO and thus no data can currently be written to the FIFO).
With known FIFO architectures, there is no way to execute a speculative unload (i.e., an unload based on a likelihood that the unloaded data will be needed at the time that it is unloaded) because once the data has been unloaded from the FIFO the state of the FIFO is lost. There is no way to reload the data into the FIFO due to the fact that all writes must occur at the end of the input stream of data, rather than at the beginning of the stream of data, which is where the unloaded data would need to be so that it would be the first data read in the next read cycle.
With current FIFO architectures, the FIFO control signals can arrive at the FIFO late without violating timing requirements. This span of time before the FIFO control signals must be valid is of sufficient length to enable a determination to be made as to whether unloading the last data from the FIFO was the proper course of action. In other words, if a speculative unload occurred, a determination could be made as to whether the unloaded data was needed when it was unloaded. However, with current FIFO architectures, speculative unloads are not performed because there is no way to put the data back into the FIFO at the location that it needs to be in the event that the unloaded data was not needed at the time that it was unloaded.
Accordingly, a need exists for a FIFO that enables the last data unloaded from the FIFO to be placed back in the FIFO in such a way that the data placed back in the FIFO is the first data unloaded from the FIFO on the following read cycle. By providing a FIFO with this capability, speculative unloads of data from a FIFO are made possible.